LP Filter & Exposures

[Mav359]

Hi Guys

I bought a from FLO a 1.25" T-Mount Camera Adapter so i could use my LP filter a Baader Neodymium Filter. Great however it seems to have made things worse.

Ive attached a JPG of a single 2min sub that has had the RGB aligned but the corners of the shot are fried and then there's a central glow.

Am i using it wrong?

[Spikey]

That looks like bad vignetting, have you stacked the rest and used flats ?

[Mav359]

Right not ideal but....

...i stacked the LIGHTS and the BIAS files, strangely i can't find my DARKS i done a quick process an had to crop the image. I'm set up now to take FLATS but hadn't in this session because I'm still learning about how to take them and use them.

As you can see i can remove most of that glow but i reckon the image is too dark as a result of trying to remove that glow thus losing data. Also attached is my first attempt at a FLAT file, i need to use the AV setting on my camera apparently which will take better FLATS but looking at that compared to the original photo will DSS for instance subtract the FLATS taking care of this glow?

Pretend for a moment if you will that i know nothing of vignetting and explain to me as you would a five year old what it means and how do i resolve it!

Cheers Spikey

[Spikey]

Hi Alan, vignetting is as you see it in your sub, very bright hotspot in the centre and darkening off to the edges. Althought in this case it looks a bit more extreme than usual. Have you tried subs without the filter in place ? I think it may need a bit of experimentation and swapping bits about to resolve.

Are you using APT for Canon camera control? I find it pretty easy to take flats with APT helping me along. You're adice is correct set the camers to Av for flats and it will take care of the exposure, just make sure the histogram appears about two thirds of the way up. DSS should be able to remove or at least minimise the vignetting.

[Mav359]

Yeah I've only ever tried without the LP filter before now, i didn't have this issue. The problem of LP was an issue but one that could fixed in photoshop, i assumed the LP filter would help.

The only other difference is that until last week my camera was damaged and the only way i could take astro-photos was to use a remote switch. I've a new camera now so the computer, in this case Nebulosity 3 is controlling the camera, i don't see how that could cause the issue though.

I'm unsure what your referencing when you speak of APT? but above is how i control the camera

Hopefully if the forecast is accurate it will be clear tonight so i'm going to try again without the filter and see what happens.

[Spikey]

Nebulosity is a good package but expensive for just running a DSLR off, future proof though.

APT is astro photography tool for controlling Canon cameras Backyard EOS is another software package for controlling Canon also.

It almost as if the LP filter isn't screwed down all the way? Moving to 2" fittings would definately help.